Air Gun Home :: View topic

turtlemann14 · Member

gun questions :/

1st, if i have a barrel that has 1 cubic inch of area, how many cubic inches of 3500psi air will i have to put down the barrel so that there will be ~3500psi behind the pellet?(assuming that there would be no restriction from valves of a smaller diameter fitting)
should i just make it so that the charge is 1.25 times the volume of the barrel?

2nd, what would be the best type of seal for a piston that would pump that high? (~3500psi)
i don't thing rubber o rings would hold up to that Mr. Green

broommaster2000 · Moderator

You want a one shot airgun using 3500 PSI as a working pressure? I think that's just really stupid, if you ask me. To keep that power under control you at least need a huge (LONG)barrel, heavy projectiles, enough knowledge of how to make ventiles, valves, etc.

Else, it'd be like making a rifle out of straws and then strapping a hand grenade to it as the ignition for the projectile.

3500 PSI (That's 241 BAR, kids) , that's not something to joke around with...

fritz · Silver Status Member

Just try working with 2000psi first, using a higher volume of air. You can get some pretty high numbers if you work it right.

aircube · Veteran Member

Are you an engineer? If not, you have a very good chance of grenading yourself Neutral

turtlemann14 · Member

no, no engineer

but i can find examples and make educated guesses and if not look some stuff up and calculate
(most of it would be over build)

most of the gun would be made out of steel (yea, pretty heavy but i would need that weight to counter act the piston)

the barrel would be the only part that i would be scared of exploding (because i was going to try to buy one with riffling in it)

can you tell me the difference in barrel length?
i was thinking about making one that was about 2 - 3 foot long if i can't find on that can hold the pressure
how hard is it to riffle the barrel?

yea, i know its unpractical to have a gun with that much pressure behind it, but i love things that are unpractical.
so please if you can, just answer my questions and give me as many tips as possible.

can you give me a general velocity for 2000psi? in .22

kanyon · Silver Status Member

To build a PCP useing 3500psi is no big drama as some will tell yer..
3500psi is NOT a lot of pressure....20,000psi plus HYD systems are high pressure......The avarage PCP air tube ..I bet has a fail pressure off over twice is working pressure...HYD tube has a fail pressure 6 times its working pressure.. 3000 working = 18,000 fail
A tube of around 32mm to hold 3500psi could be made from a length
of 2mm "83thou" wall 3140 tube "chrome molly"...
The more psi you use the smaller the valve head will need to be as the
hammer spring has to be able to work against the valve spring & air tube psi........And in there lies the prob...just because theres 3500psi in the tube don't think that is what is going to come out though the valve...
most PCPs only release around 2000 /// 2500 for the higher powered ones...."valve size opening time" Thats why you can get 30 plus ful power shots from some PCPs....
If it let is full psi out in the first shot the gun would only get one full power shot and every shot after that would be less than the last...

my Evanix AR6 is a good exsample.... 65FPE but only good for 12/15 full power shots...fill psi is 3000 but once it drops down to around the 2400psi
the power drops off.....but even after that its still got more power than a lot of PCPs and any springer.....

If yer want to build a 3500psi go for it...theres no reassion engineering or saftey wise that should stop yer........3500psi is not a bomb if its housed correctly

Pete

broommaster2000 · Moderator

kanyon · Silver Status Member

broommaster2000 · Moderator

23ib0d0n · Moderator

1100psi was enough to destroy this building, etc . . .

http://www.scubabomb.freeservers.com/Cscuba.htm

Always good to know what the differences are between a hydraulic failure and a pneumatic failure . . .

http://www.scubabomb.freeservers.com/

dummyracer36 · Senior Member

hell, i've seen home sized air compressors with a faulty auto shut off burst @ under 200 psi taking out walls.

as for turtle's initial questions... i just dont think he fully understands how PCP rifles operate. if he wants to take the time and learn the principals, great... thats how some small gunsmiths got their start, and theres more than a few of those... Dennis Quackenbush comes to mind.

AirGunEric · Site Admin

Let's review;

"Cubic inches" is not a measurement of "area" but of "volume". If you have one cubic inch, and 3500psi (pounds per square inch) -i.e. pressure/force the two are not directly compatible. If you have a 13ci 3500psi air tank, it will fill such a gun's barrel 13 times (actually less, diminishing pressure in the tank as an amount is removed- so more likely something like 8 full-volume fills of the barrel).

Anyways, I also don't understand the idea of a 'piston' and a PCP- these are two different concepts. You wouldn't need a piston in a PCP setup, only a valve.

"Seals" as I think they are being stated here are not holding such pressures back- the "seal" is accomplished with solid surfaces being stuck together (i.e. two pieces of steel that are mated to one another) with a gasket/"seal" between the surfaces that is compressed significantly to take up any imperfections between the two solid mating surfaces.

As to pressures- any attempt at building a system with full 3500psi charges needs to be engineered properly with the correct materials or that "scuba bomb" idea could become a reality.

Keep in mind that it's not necessarily "pressure" that will work, but "volume"- if you can get a large enough volume behind a large projectile, the pressure could be much lower to make this work. I think the idea of building prototypes with very low pressures (i.e. a couple hundred PSI maximum) would be a great educational exercise before attempting to eat the whole elephant.

Edited- too many typos

dummyracer36 · Senior Member

turtlemann14 · Member

the ci is the amount of highly compressed air i will have

the piston in the gun would use surface area to boost 125 psi to 3500psi (at the sacrifice of volume)

there will be no tank other than the 125psi air compresser, the rest will be inline with the barrel and buried behind at least 3/8" of steel, it will probably end up being something like 1/2" or a little more

i have access to a full machine shop and a CNC mill and (hopefully) a CNC lath. we have many manual lathes.

low pressure and high volume means that it would take a long barrel to get it moving to speed
(although i am sure that it would be much more stable that way)

the "gun" in the picture was just a 5 minute screw around toy(you just dump the bb's in and blow air though it)

as for the scuba tank failures, those are high capacity vessels compared to what i want to make(the high pressure air is not even stored in the gun, the only air stored in the gun would be 125psi)

psi = pressure per square inch
the less surface area there is, the less pressure on the area
and my bike tires take 65 psi (less surface area)

i thought co2 was only good for 600 psi?

i will try to get a drawing of the gun so you guys can get an idea of where i am going with this, as i think i am confusing a bunch of you with the piston idea
who knows you might even want to employ this idea

Rogerflat · Silver Status Member

Turtlemann, you are either significantly smarter than most of us, or you will be a future explosion victim.

I remember not wanting to get a pcp due to the complexities of compressed air tanks, pumps, valves, etc. I was also a little fearful of something going wrong and being injured.

And sure enough, they send me my talon and it didn't hold air. After time, money, and frustration I finally got it fixed, but the point is that when you are dealing with complex systems, and things that are inherently dangerous....sh*t can happen.